Compressible plunger for hypodermic syringes



1959 E. s. v. LAUB 2,907,330-

COMPRESSIBLE PLUNGER FOR HYPODERMIC SYRINGES Filed June 10, 1958 I till 1,011,111]! I I2 I 3 ill/III.

Ernesr S V. Ldub INVENTOR.

United States Patent G F COIVIPRESSIBLE PLUNGER FOR HYPODERMI SYRINGES Ernest S. V. Laub, Corona del Mar, Calif.

Application June 10, 1958, Serial No. 741,027

Claims. (Cl. 128-218) This invention relates to hypodermic syringes and more particularly relates to an improved plunger construction for such and similar instruments.

While a hypodermic syringe may appear to be a comparatively simple instrument, consisting essentially of a cylinder with hollow needle and a plunger fitting the cylinder and slidable therein to expel the contents thereof through the needle, a vast amount of time is consumed in fitting the parts together, either when they have just been manufactured or when they have been taken apart for sterilizing or for any other reason. When all syringes were made of glass, the cylinders were cast and the plungers were ground to fit particular cylinders. The corresponding, exactly fitted parts were sometimes given like numbers, to assist in matching them. These numbers might have five, six, or even seven digits, and sorting a trayful of them was not easy or quick. Later, with the advent of plastic materials, the like-sized parts might be given group numbers or letters; that is, all cylinders between a minimum and a maximum might have a certain code, and all plungers that might fit those cylinders might have the same code. But that system still requires a great deal of trial-anderror fitting within the same code, before approximate mates were found.

In terms of broad inclusion, this invention comprises molding plunger heads out of plastic material which has a slight amount of elasticity and in forms which permit the plunger head to contract under pressure when forced into a cylinder. Rubber plunger heads or rubber-sealed plunger heads are, of course, old, but rubber greatly increases the friction and the force necessary to operate the syringe, a force too easily misapplied to the needle in the hands of an operator lacking in skill. Cup-shaped plunger heads having the cup rim on the pressure, or liquid, side, whereby the cup-rim is spread by the increase of pressure, not only unnecessarily increase the friction but also hold a part of the syringe contents in an undeliverable manner. By employing plunger heads of plastic having a definite but low amount of elasticity and also a low amount of friction, and by building them with hollow zones into which they may be compressed, those hollow zones opening rearwardly into air rather than forwardly into liquid and thereby not tending to cause expansion under pressure, I have succeeded in making syringes in which a given cylinder will fit plungers having a very considerable difference in diameter, and still stay leak-proof.

A principal object of my invention is to provide, for use with a cylinder of a given size, a slightly over-size plunger which is easily compressible and may therefor be used with other cylinders which vary in diameter within the limits of the plungers compressibility.

It is another object of my invention to provide a plunger having a low friction with the associated cylinder and yet a tight seal therewith.

A further object of my invention is to provide a plunger which does not expand and thereby increase the friction and the pressure necessary for operation when it is patented Oct. 6, 1959 pressed into the cylinder, but maintains an even pressure against the cylinder Walls.

Still another object of my invention is to provide a plunger which may easily be sterilized, particularly on that face which is in contact with the syringe contents.

In the accompanying drawing, I have shown my improved plunger as part of a syringe of the general type disclosed in my co-pending application for patent, Serial No. 705,361, but it is to be understood that my new plunger may beused with other types of cylinders and may be modified in its locking and rotating aspects to conform to other cylinders.

Fig. 1 of the drawing is a longitudinal sectional view,

' showing the plunger retracted in the cylinder, and the needle protected by a guard;

Fig. 2 is an end elevation, as seen from the left in Fig. 1; Fig. 3 is a longitudinal sectional View on the line 33 of Fig. 1, and on an enlarged scale;

Fig. 4 is a transverse sectional View on the line 44 of Fig. 3;

Fig. 5 is a transverse sectional view of a modified form of plunger; and

Fig. 6 is a transverse sectional view of still another modification of the plunger.

Having reference now to the details of the drawing, I have shown in Fig. 1 a cylinder 10 having an open end 11 and a closed end 12. From the closed end 12 there protrudes a hollow needle 13, sealed by a seal 14. The cylinder 10 is preferably made of a grade of plastic which will withstand autoclaving but other materials may also be used. Keyways 15 extend longitudinally of the cylinder 10 from the open end 11to a point approximately half-way to the closed end 12. Two such keyways 15 are shown in Figs. 3 and 4. The open end 11 is rimmed by laterally outstanding flanges 16 on one side of each of the keyways 15; on the opposite side, the wall of the cylinder 10 extends beyond the flanges 16 and forms stops 17 which stop rotation of a plunger 20. The corners 18 of the flanges 16 are rounded to permit a cam action by a member sliding across them.

The plunger 20 has, at its outer end 21, keys 22 which fit slidably within the keyways 15. The keys 22 extend The plunger 20 is preferably of two-piece construction and comprises a base section 25 which includes the keys 22 and fingers 23, and a plunger head 26. The head 26 is joined to the base section 25 by a tenon 27 which enters a mortise 28. The head 26 is preferably made of a plastic having the qualities of a slight elasticity, permitting a moderate degree of displacement under pressure, and of recovery when pressure is released. A plastic having suitable qualities is manufactured by Phillips Petroleum Company and is sold under the trade name of Marlex. However, I do not limit myself to the use of Marlex in my invention, as new plastics are constantly being brought out, having desirable qualities.

The tenon 27 may be secured in the mortise 28 by any desirable means, such as by heat, or by friction, or by chemical or physical means such as adhesives or plastics which re-act upon the plastics of theplunger, or by riveting the base 25 through the mortise 28 into the tenon 27.

The head 26 is of such diameter as to require forcing 30is termed the rearward end of the plunger.

separately, may be considered as constituting a neck 29 upon which the head 26 is mounted. Preferably the tenon 27 is a little long for the mortise 28 into which it fits, and thereby it holds the rearwardly facing annular shoulder 39' of-thehead'26 spaced from the base section 25*by an annular air-space 31.

For the purpose of definition, the face 32 of the plunger head 26 which enters the cylinder'ill first is herein termed the forward end of the plunger, and the annular shoulder The face 32 may advantageously berounded, as at 33, where it joins the cylindrical surface 34, of greatest diameter, of the head 26.

In the preferred form of my invention, illustrated in Figs. -3 and 4, a plurality of concavities 35 are formed in the head 26, opening rearwardly at the annular shoulder 30 and extending forwardly approximately to the forward limit of the cylindrical surface 34. These concavities are in the nature of slots, separated by webs'36, and do not pierce the forward face 32, but terminate within the rounded shoulders 33. Their purpose-is to permit compression of the cylindrical wall 34 so that the plunger head 26 may be pushed to the closed end .of the cylinder 10. 35 will not fill with liquid held in the cylinder 10, but are open rearwardly to air. Furthermore they will not cause the cylinder'wall 34 to expand and increase friction when pressure is applied to push the plunger into the cylinder, but on the contrary theypermit radially inward displacement of the plunger wall and a diminution of friction.

In Fig. I have shown a modification of my invention in which the concavities are a plurality of round holes37, rather than slots, and are spaced apart with webs '38 so thin as to yield easily to permit inward radial displacement of-the outer wall.

A further modification is shown in Fig. 6 in which the webs 36 or 38 are dispensed with altogether, and the concavity 39 extends annularly between the outer wall 34 and the core 40 of the plunger.

In the manufacture of my improved syringe, it is only necessary to make a cylinder of an established max imum inner diameter. All plungers 20 having heads 26 of that maximum diameter, or slightly larger, are able to fit the given cylinder or cylinders of slightly less inner diameter. Thus, practically, a universal fit, ranging It will be noted that the concavities around a given stated size is established. For example ifa cylinderbe listedas 'having'aninternal diameter of one centimeter, it may havean inward variance of 0.003 or more centimeters, and be actually 0.997 centimeter or less in internal diameter, and yet receive all plungers from one centimeter in head-diameter to about 1.01 centimeters, without leakage, and without unduly increasing friction.

"The disclosed embodiments are not to be-construed as limitations upon my' invention, the scope of which is deemed to include any desirable constructive'modification within the spirit and breadth of the appended claims.

I claim:

1. In a syringe, including a cylinder: 21 plunger having a head of elastic material 'of slightly larger diameter than the internal diameter of said cylinder, and having a neck of restricted diameter, said head having a zone of concavity adjacent said neck and opening toward said necksparallel to said neck, intowhichsaid'headds-tiompressively displaceable .to diminish'the diameter :of said head.

'2. In a syringe,'including a cylinder: aplunger having ahead of elastic-plasticmaterial of'such diameter-as to require:forcing into said cylinder, and having a neck of restricted diameter rearwardly of said head, said head havinga-rearwardly extending cylindrical wall defining the outer rside of a concavity opening rearwardly and parallel to said neck to receive-radial'inward displacement of said wall.

3. Ina syringe, a plunger as set forth 'in claim 2, in which said concavity is intermittent-and divided by web portions joining said rearwardly extending wall of said headr-with the central portion of said head.

4. In a syringe, a plunger, as set forth in claim '2 in which said rearwardly extending wall terminates in an annular shoulder radial to said neck, and'said concavity consists in a plurality of cavities entering said head from said'shoulder.

5. In a syringe, a plunger as set forth in-c laim 2, in which said concavity is annular.

References Cited inthefile ofthis patent UNITED STATES PATENTS 

